Follow node A: Change seed to 2

1. SSCH: Improving the Capacity of IEEE 802.11 Multihop Networks Using Slotted Seeded Channel Hopping Follow node A: Change seed to 2 Victor Bahl, Ranveer Chandra and John Dunagan Motivation SSCH Description SSCH Performance Slotted Seeded Channel Hopping On a single IEEE 802.11 channel, only one transmission can take place at a time. • In the QualNet simulator, we used the following: • A channel switch time of 80 µs. • A slot duration of 10 ms. • IEEE 802.11a with 13 channels at 54 Mbps. 1) SSCH Seeds Problem: Nodes can communicate only when they overlap 1) SSCH Microbenchmark Solution: Allow sending nodes to follow the receiver. So we use pseudo-random instead of random choices. Effect of a parallel session, and node mobility. New Channel = (Old Channel + seed) mod (# Channels) seed is from 1 to (# Channels -1) • Protocol: • Each node periodically broadcasts (channel, seed) pair. • If node B has a packet to send to node A, it will adjust its (channel, seed) • B resets seed after it is done sending the packet. Simultaneously transmitting on all the orthogonal channels will significantly improve network capacity. 1 0 2 1 0 2 1 0 Design Constraints A: Seed = 2 • Unmodified IEEE 802.11 when not switching Easy to deploy with legacy cards. • One radio per node Lesser power consumption. • No logical partitions Ensure that any two neighboring nodes are not partitioned due to channel switching. 0 1 2 1 0 2 1 0 B: Seed = 1 2) SSCH Slots • Loose clock synchronization Tight clock synchronization is difficult in multihop networks. • Significant capacity improvement The protocol should give a significant capacity gain with respect to IEEE 802.11. 2) SSCH System Throughput Problem: Nodes can follow only one other node. Solution: Nodes have multiple seeds. Each seed can be synched to a different node. On varying the number of disjoint flows in the network. Problem: Nodes with the same seeds might not overlap Solution: After cycling through all slots and all channels, a node has a parity slot. In this slot, the channel number of the node is the sum of all the seeds. Basic Approach • Divide time into slots • Cards switch to a randomly selected channel at the beginning of a slot. If the number of channels is 3, and a node has 2 seeds: 1, 2 (2 + seed 2) mod 3 For 3 channels: 1 2 1 1 3 2 3 3 1 2 2 1 0 0 0 1 2 2 1 0 0 Parity Slot = (seed 1 + seed 2) mod 3 (1 + seed 1) mod 3 3) Other Results 3 2 1 3 1 2 1 3 Mathematical Properties Communicating nodes stay synchronized, and there is an infrequent overlap between silent nodes. SSCH also avoids logical partitions. SSCH performs better than single channel IEEE 802.11a with MANET routing protocols in mobile multihop networks. With a high probability any two nodes will overlap on a channel in a slot within a certain period.